So I've had my sorority tank for almost a month now and 5 out of 6 of the girls I have there are acting perfectly normal. I'm concerned for one girl I have who I have not seen eat once in the whole time I've had this tank. I bought her at the same time as 3 other of the girls, all whom are eating just fine. None of my other fish have stress stripes, just this one in particular. I've watched them before, and none of the girls fight with each other. In fact, she hangs out on her own in the back corner most of the time, while the rest of the gang swims around near the top or middle section a lot. What's wrong with my betta that's causing this loss in apetite? ):

Housing
What size is your tank? 10g
What temperature is your tank? 80˚F
Does your tank have a filter? Yes
Does your tank have an air stone or other type of aeration? Just water dropping from HOB filter.
Is your tank heated? Yes
What tank mates does your betta fish live with? 5 other female bettas

Food
What type of food do you feed your betta fish? Betta fish pellets
How often do you feed your betta fish? Everyone's fed once a day

Maintenance
How often do you perform a water change? Once a week
What percentage of the water do you change when you perform a water change? 25%
What type of additives do you add to the water when you perform a water change? Water conditioner and ammonia/nitrate/nitrite detoxifier.

Symptoms and Treatment
How has your betta fish's appearance changed? Looks the same since I bought her, stress stripes.
How has your betta fish's behavior changed? Mainly hangs around near the bottom while all the other fish spend most of their time near the top.
When did you start noticing the symptoms? Ever since I bought her.
Have you started treating your fish? If so, how? No
Does your fish have any history of being ill? No
How old is your fish (approximately)? Probably less than a year old.

Adding more plants can help reduce stress, but if she is this stressed out I would give her own tank see if she eats or is less stressed.
Sometime fish just don't do well in a sorority for no apparent reason, they just don't like other fish.

Anther idea is you could temporarily cup her at feeding time, so you can make sure she's getting enough food. Perhaps if she gets nice and fat she'll feel confident enough to handle being around the others? But if she's got stress stripes most of the time, a second tank just for her is probably the best way to go if you can swing it.